Maintaining consistency for remote copy using virtualization

ABSTRACT

Provided are a system and article of manufacture for copying storage, wherein a first unit receives data updates from a second unit. The data updates are stored in a plurality of physical storage locations associated with the first unit. Links are generated to at least one of the plurality of physical storage locations to achieve consistent data between the first unit and the second unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 10/754,231filed on Jan. 9, 2004, which is incorporated herein by reference in itsentirety.

Application Ser. No. 10/754,231 filed on Jan. 9, 2004 was related to thefollowing co-pending and commonly-assigned patent application filed onthe same date as the filing date of application Ser. No. 10/754,231, andwhich is incorporated herein by reference in its entirety: “OrderingUpdates in Remote Copying of Data,” having attorney docket no.SJO920030037US1.

BACKGROUND OF THE INVENTION

1. Field

The present disclosure relates to a method, system, and an article ofmanufacture for maintaining consistency for asynchronous remote copyusing virtualization.

2. Description of the Related Art

Information technology systems, including storage systems, may needprotection from site disasters or outages. Furthermore, informationtechnology systems may require features for data migration, data backup,or data duplication. Implementations for disaster or outage recovery,data migration, data backup, and data duplication may include mirroringor copying of data in storage systems. In certain information technologysystem, data is copied from a primary storage control to a secondarystorage control. In response to the primary storage control beingunavailable, the secondary storage control may be used to substitute theunavailable primary storage control.

Data copying in information technology systems may be synchronous orasynchronous. Synchronous copying involves sending data from the primarystorage control to the secondary storage control and confirming thereception of such data before completing write operations to the primarystorage control. Synchronous copy, therefore, slows the write operationresponse time while waiting for the confirmation from the secondarystorage control. Synchronous copy, however, provides sequentiallyconsistent data at the secondary storage control.

Asynchronous copy may provides better performance than synchronous copybecause the write operation to the primary storage control may becompleted before the reception of sent data is confirmed from thesecondary storage control. However, data sequence consistency may haveto be ensured since data received at the secondary storage control maynot be in order of the updates, i.e., write operations, to the primarystorage control. In asynchronous copy, cross-device consistency betweenthe primary and the secondary storage control may be achieved by storingupdates temporarily in a hardened location, such as a journal dataset,until a set of consistent updates is available to apply to the secondarystorage associated with the secondary storage control.

SUMMARY OF THE PREFERRED EMBODIMENTS

Provided are a method, system, and article of manufacture for copyingstorage, wherein a first unit receives data updates from a second unit.The data updates are stored in a plurality of physical storage locationsassociated with the first unit. Links are generated to at least one ofthe plurality of physical storage locations to achieve consistent databetween the first unit and the second unit.

In additional embodiments, the first unit is a secondary storage controlcoupled to a secondary storage and the second unit is a primary storagecontrol coupled to a primary storage, wherein the plurality of physicalstorage locations are associated with the secondary storage, and whereinthe data updates are received asynchronously at the first unit.

In further embodiments, the received data is stored only once in theplurality of physical storage locations associated with the first unit,and unlinked physical storage locations are released to be used forstoring subsequent data updates.

In yet additional embodiments, an application sends input/outputrequests to the second unit, wherein the data updates correspond tooutput requests from the application, and wherein the data updates arestored only once at the first unit, wherein the first unit cansubstitute the second unit in responding to the input/output requestsfrom the application at any point in time, and wherein data in the firstand second units are consistent at all points in time.

In yet further embodiments, a determination is made as to whether thestored data updates form a consistency group, prior to generating thelinks. A waiting is performed to receive a next data update in responseto the stored data updates not forming a consistency group.

In yet additional embodiments, a determination is made as to whether thestored data updates form a consistency group, prior to generating thelinks. A determination is made of the at least one physical storagelocation that commits the consistency group, wherein virtual storageassociated with the first unit links to the determined at least onephysical storage location.

In further embodiments, a data structure that maps virtual storagelocations to the at least one of the plurality of physical storagelocations is maintained, wherein the generated links are associated withthe data structure, and wherein a plurality of applications are capableof performing input/output operations with the virtual storagelocations.

In additional embodiments, data structures representing consistencygroups corresponding to the data updates are maintained, wherein themaintained data structures are capable of pointing to the plurality ofphysical storage locations. A deletion is performed on a first datastructure that represents a first consistency group in response to firstdata updates associated with the first consistency group beingcommitted.

In further embodiments, an error is received, at the first unit, inresponse to waiting for a data update. The generated links are modifiedto reflect consistent data between the first unit and the second unit.

Certain embodiments achieve consistency for asynchronous remote copyusing a virtual storage system. A replication management applicationwrites data that has been received but that is not yet consistent withdata associated with other storage controls into unused physicalstorage. In response to data necessary to provide consistency beingreceived, virtualization tables may be updated at the true secondarylocations to point to locations in the physical storage where the datahas been written. In certain embodiments, the received data at asecondary storage control may be written only once to the physicalstorage associated with the secondary storage control.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers representcorresponding parts throughout:

FIG. 1 illustrates a block diagram of a computing environment, inaccordance with certain described aspects of the invention;

FIG. 2 illustrates a block diagram of data structures and devicesrelated to the computing environment, in accordance with certaindescribed implementations of the invention;

FIG. 3 illustrates a block diagram of consistency groups, in accordancewith certain described implementations of the invention;

FIG. 4 illustrates logic for maintaining consistency usingvirtualization, in accordance with certain described implementations ofthe invention;

FIG. 5 illustrates a block diagram of a first state of data structuresin an exemplary embodiment, in accordance with certain describedimplementations of the invention;

FIG. 6 illustrates a block diagram of a second state of data structuresin an exemplary embodiment, in accordance with certain describedimplementations of the invention;

FIG. 7 illustrates a block diagram of a third state of data structuresin an exemplary embodiment, in accordance with certain describedimplementations of the invention;

FIG. 8 illustrates logic for logic for maintaining consistency anddisaster recovery, in accordance with certain described implementationsof the invention; and

FIG. 9 illustrates a block diagram of a computer architecture in whichcertain described aspects of the invention are implemented.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanyingdrawings which form a part hereof and which illustrate severalimplementations. It is understood that other implementations may beutilized and structural and operational changes may be made withoutdeparting from the scope of the present implementations.

FIG. 1 illustrates a block diagram of a computing environment, inaccordance with certain aspects of the invention. A primary storagecontrol 100 is coupled to a secondary storage control 102. Anapplication system 104 that includes one or more applications mayperform I/O operations, including write operations, to the primarystorage control 100. In certain embodiments the application system 104may reside in a host computational device that is coupled to the primarystorage control 100 via a host bus adapter.

The primary storage control 100 and the secondary storage control 102may store and retrieve data from a primary storage 106 and a secondarystorage 108 respectively, where the primary storage 106 is coupled tothe primary storage control 100 and the secondary storage 108 is coupledto the secondary storage control 102. Additionally, the primary storagecontrol 100 and the secondary storage control 102 may control theoperations of the primary storage 106 and the secondary storage 108respectively. The primary storage 106 and the secondary storage 108 mayinclude non-volatile storage, such as, hard disk drives, RAIDs, directaccess storage devices, or other types of physical storage.

In certain embodiments, the primary storage control 100 may not beoperational and data associated with the secondary storage control 102may be used by a recovery system 110 for processing. In embodiments ofthe invention, data associated with the secondary storage control 102 ismaintained consistent with data associated with the primary storagecontrol 100. The consistency is maintained by a replication managementapplication 112.

The replication management application 112 is coupled to the primarystorage control 100 and the secondary storage control 102 and in certainembodiments may mirror data from the primary storage control 100 to thesecondary storage control 102. In some embodiments, the mirroring may beperformed by copying data asynchronously from the primary storagecontrol 100 to the secondary storage control 102.

In certain embodiments, the replication management application 112 maybe spread across the primary storage control 100 and the secondarystorage control 102. In other embodiments, the replication managementapplication 112 may reside on a separate system that is different fromthe primary storage control 100 and the secondary storage control 102.In yet additional embodiments, the replication management application112 may reside in only one of the primary storage control 100 and thesecondary storage control 102.

In certain embodiments, the replication management application 112maintains consistency of data updates received from the applicationsystem 104, where the data updates are asynchronously copied to thesecondary storage control 102 from the primary storage control 100. Thereplication management application 112 may perform a virtualization ofthe secondary storage 108 that is coupled to the secondary storagecontrol 102 to maintain the consistency of data across the primarystorage control 100 and the secondary storage control 102. In certainembodiments, virtualization includes the mapping of the physicalsecondary storage 108 to virtual volumes.

Therefore, FIG. 1 illustrates an embodiment where the replicationmanagement application 112 virtualizes the secondary storage control 102and maintains consistency of data across the primary storage control 100and the secondary storage control 102, where data is copiedasynchronously from the primary storage control 100 to the secondarystorage control 102.

FIG. 2 illustrates a block diagram of data structures and devicesrelated to the replication management application 112 and the secondarystorage control 102, in accordance with certain describedimplementations of the invention.

The secondary storage control 102 may receive data updates 200 generatedas a result of write operations from one or more applications 204 a . .. 204 m to the primary storage control 100, where the one or moreapplications 204 a . . . 204 m may comprise the application system 104.In certain embodiments, the data updates 200 from the application system104 arrive asynchronously at the secondary storage control 102 via theprimary storage control 100 and the data updates 200 may be referred toas a data update stream.

The replication management application 112 creates one or more virtualdevices, such as, virtual volumes 206 a . . . 206 n associated with thesecondary storage control 102. The primary storage control 100 may alsohave virtual volumes that correspond to the virtual volumes 206 a . . .206 n. In certain embodiments, the data corresponding to the virtualvolumes 206 a . . . 206 n are stored in locations in the physicalsecondary storage 108. The mapping of the virtual volumes 206 a . . .206 n to locations in the physical secondary storage 108 may be storedin virtualization tables 208 associated with the secondary storagecontrol 102. In certain embodiments, the virtualization tables 208 maybe coupled to the virtual volumes 206 a . . . 206 n.

The application system 104 performs I/O operations with respect tovirtual volumes associated with the primary storage control 100 andcorresponding virtual volumes 206 a . . . 206 n are also associated withthe secondary storage control 102.

In certain embodiments, the replication management application 112 mayinclude a consistency group determination application 210, andassociated data structures corresponding to consistency groups 212.

Therefore, FIG. 2 describes an embodiment where the replicationmanagement application 112 virtualizes the secondary storage control 100and maintains data consistency across the primary storage control 100and the secondary storage control 102.

FIG. 3 illustrates a block diagram of exemplary consistency groupscreated by the replication management application 112, in accordancewith certain described implementations of the invention.

A consistency group is a set of updates in which the updates may span aplurality of storage volumes, and where the updates must be writtentogether in order to maintain mutual data consistency between the datacontained in each storage volume of the plurality of storage volumes. Toprovide a non-limiting example, a first command copies volume A1associated with the primary storage control 100 to volume B1 associatedwith the secondary storage control 102 and a second command copiesvolume A2 associated with the primary storage control to volume B2associated with the secondary storage control. It is required thatvolumes B1 and B2 should represent a consistent state of the dataset involumes A1 and A2 at a certain point in time. In a certain sequence ofoperations on the volumes the following set of dependent writeoperations by the application system 104 may occur (where the secondoperation occurs after the first operation):

1. Write to dataset on volume A1 (data updated)2. Write to dataset on volume A2 (data updated)

When volumes A1 and A2 are asynchronously copied to volumes B1 and B2respectively via the data updates 200, then the following non-limitingexample of a sequence of operations may create an inconsistent state involumes B1, B2 with respect to volumes A1, A2.

1. Copy volume A1 to volume B12. Write to dataset on volume A1 (data updated)3. Write to dataset on volume A2 (data updated)4. Copy volume A2 to volume B2At the conclusion of all the copy operations, i.e., the conclusion ofthe fourth operation, volume B2 contains the data update of volume A2whereas volume B1 does not contain the data update of volume A1. The setof volumes B1, B2 are in an inconsistent state with respect to the setof volumes A1, A2. An application 204 a . . . 204 m that uses thevolumes B1, B2 associated with the secondary storage control 102 couldnot recover from a back-up copy stored in the volumes B1, B2.

Therefore, not all sequence data updates can form a consistent set ofdata updates. In FIG. 3, the rows of table 300 represent differentdevices and the columns represent different times. The times arerelative times and not absolute times. For example, t3 (referencenumeral 306) is a time after t2 (reference numeral 304), and t2(reference numeral 304) is a time after t1 (reference numeral 302). Aletter-number combination in the body of the table 300 identifies anupdate to a device at a time, with the letter identifying an applicationand the number a sequence of updates for the application. For example,B1 (reference numeral 308), is the first data update from an applicationnamed B, where the update is for the device D3 (reference numeral 310)that arrives at relative time t1 (reference numeral 302). The differentshadings in the entries of the table 300 identify a data-consistent setof updates, and may not necessarily be just vertical slices of entriesin the table. For example, the table 300 has three consistency groups312, 314, 316. The update data in a consistency group may need to beapplied together to the secondary control 102 for data associated withthe secondary control 102 to remain consistent with data associated withthe primary control 100. The determination of consistency groups 312,314, 316 in the table 300 may be performed in any manner known in theart.

Therefore, FIG. 3 illustrates an embodiment of exemplary consistencygroups 312, 314, 316 that may be generated by the replication managementapplication 112 by processing the data update stream 200 that arrivesasynchronously at the secondary storage control 102 from the primarystorage control 100. For preserving data consistency with the primarystorage control 102, first a consistency group is determined andcommitted, and then the data updates of the consistency group arereflected via pointers or links in the virtual volumes 206 a . . . 206 nof the secondary storage control 108.

FIG. 4 illustrates logic for maintaining consistency usingvirtualization as implemented in the secondary storage control 102 inaccordance with certain described implementations of the invention.

Control starts at block 400, where the replication managementapplication 112 creates virtualization tables 208 corresponding to thevirtual volumes 206 a . . . 206 n associated with the secondary storagecontrol 102, where the virtualization tables 208 point to locations inthe physical storage 108 and may define the consistent data contents ofthe virtual volumes 206 a . . . 206 n. The consistency of the datacontents of the virtual volumes 206 a . . . 206 n is with respect to thedata contents associated with the primary storage control 100.

The replication management application 112 receives (at block 402) adata update 200 for a virtual volume 206 a . . . 206 n associated withthe secondary storage control 102. For example, in certain embodimentsthe data update 200 may be the data update B1 (reference numeral 308).

The replication management application 112 writes (at block 404) thedata update 200 into unused physical storage. For example, thereplication management application 112 may write the data update 200into unused locations of the secondary storage 108.

The replication management application 112 determines (at block 406) ifall data updates for a consistency group 212, such as, consistencygroups 312, 314, 316 have been received. If so, the replicationmanagement application 112 updates (at block 408) the virtualizationtables 208 to point to the locations in the physical storage 108 thatdefine a commitment of the data updates included in the consistencygroup 212. The updated virtualization tables 208 define the new dataassociated with the virtual volumes 206 a . . . 206 n. The dataassociated with the virtual volumes 206 a . . . 206 n of the secondarystorage control 102 is therefore consistent with data associated withthe primary storage control 100.

The replication management application 112 frees (at block 410) space inthe physical storage 108 as a result of the updates to thevirtualization tables 208. For example, certain data updates 200 writteninto the unused physical storage performed in block 404 may not beneeded and may be freed. The replication management application 112receives (at block 402) the next data update 200.

If the replication management application 112 determines (at block 406)that all data updates for a consistency group 212, such as, consistencygroups 312, 314, 316, have not been received then the replicationmanagement application 112 receives (at block 402) the next data update200.

Therefore, FIG. 4 describes certain embodiments in which the replicationmanagement application 112 writes all data updates 200 into locations inunused physical storage 108 and after determining a consistency group212 may harden only a certain number of the written data updates byupdating virtualization tables 208 to point to the certain number of thewritten data updates. No copying of the written data updates isnecessary.

FIG. 5 illustrates a block diagram of a first state of data structuresin an exemplary embodiment, in accordance with certain describedimplementations of the invention, where original data is associated withthe secondary storage control 102 and data updates corresponding tofirst and second consistency groups have arrived at the secondarystorage control 102 but have not been committed.

In FIG. 5 a linear representation of an exemplary disk 500, such as thephysical storage 108 is shown. The exemplary disk 500 has ten physicalblocks with the first physical block containing a first virtual block(VB) named VB1 that is part of the original data in the disk 500. Asdata updates 200 arrive and are associated with different consistencygroups (CG) the data updates are written into the disk 500. For example,a data update 200 for the fourth virtual block (VB4) which is part ofthe second consistency group (CG2) is written in physical block five.The virtual blocks correspond to the virtual volumes 206 a . . . 206 n.

FIG. 5 also illustrates current data pointers 502 that point to thephysical blocks of the original data in the disk 500, a firstconsistency group pointers 504 that point to the physical blockscorresponding the data updates comprising the first consistency group,and a second consistency group pointers 506 that point to the physicalblocks corresponding to the data updates comprising the secondconsistency group.

Tables representing the virtual block to physical block mapping of thepointers 502, 504, 506 are also maintained. For example, current datapointer table 508 illustrates the current mapping of the virtual blocksto the physical blocks in the disk 500. The mapping in the current datapointer table 508 illustrates hardened or committed data, i.e., datathat is consistent across the primary storage control 100 and thesecondary storage control 102. The applications 204 a . . . 204 n thataccess data associated with the secondary storage control 102 work withthe data pointed to by the current data pointers 502.

The first consistency group pointer table 510 illustrates the mapping ofthe virtual blocks to the physical blocks in the disk 500 for dataupdates that form part of the first consistency group. The datarepresented in the first consistency group pointer table 510 is nothardened as the first consistency group has not been committed as yet.

Similarly, a second consistency group pointer table 512 illustrates themapping of the virtual blocks to the physical blocks in the disk 500 fordata updates that form part of the second consistency group. The datarepresented in the second consistency group pointer table 512 is nothardened as the second consistency group has not been committed as yet.

Therefore, FIG. 5 illustrates a first state of data structures in anembodiment where data updates 200 for the first and second consistencygroups have arrived at the secondary storage control 102 but have notbeen committed.

FIG. 6 illustrates a block diagram of a second state of data structuresin an exemplary embodiment, in accordance with certain describedimplementations of the invention, where the data updates 200corresponding to the first consistency group pointer table 510 have beenhardened, i.e., the first consistency group has been committed, anduncommited data updates 200 corresponding to a third consistency grouphave arrived at the secondary storage control 102.

FIG. 6 illustrates the updated current data pointers 502 that point tothe physical blocks of the original data in the disk 500, the secondconsistency group pointers 506 that point to the physical blockscorresponding the data updates comprising the uncommitted secondconsistency group, and a new third consistency group pointers 600 thatpoint to the physical blocks corresponding to the uncommitted dataupdates comprising the third consistency group.

Tables representing the virtual block to physical block mapping of thepointers 502, 506, 510 are also maintained. For example, current datapointer table 508 illustrates the current mapping of the virtual blocksto the physical blocks in the disk 500. The mapping in the current datapointer table 508 illustrates hardened or committed data after the dateupdates 200 of the first consistency group have been committed.

The third consistency group pointer table 602 illustrates the mapping ofthe virtual blocks to the physical blocks in the disk 500 for dataupdates that form part of the third consistency group. The datarepresented in the second consistency group pointer table 512 or thethird consistency group pointer table 602 is not hardened as the secondand third consistency groups have not been committed as yet. In FIG. 6the first consistency group pointer table 510 has been deleted as thedata updates for the first consistency group have been committed.

Therefore, FIG. 6 illustrates an embodiment where data updates 200 forthe first, second and third consistency groups have arrived at thesecondary storage control 102 and only the data updates of the firstconsistency group have been committed.

FIG. 7 illustrates a block diagram of a third state of data structuresin an exemplary embodiment, in accordance with certain describedimplementations of the invention. In FIG. 7 the data updates 200corresponding to the second and third consistency groups have beencommitted.

Since the data updates of the first, second and third consistency groupshave been committed the first consistency group pointer table 510, thesecond consistency group pointer table 512, and the third consistencygroup pointer table 602 are all shown to be deleted. The current datapointers point to physical block 5, 6, 8, 9 of the disk 500 andcorrespond to virtual block VB4, VB2, VB1, and VB3 respectively.

Therefore, FIG. 7 illustrates an embodiment where data updates 200 forthe first, second and third consistency groups have arrived at thesecondary storage control 102 and all the data updates have beencommitted.

FIG. 8 illustrates logic for logic for maintaining consistency anddisaster recovery implemented in the replication management application112, in accordance with certain described implementations of theinvention.

Control starts at block 800, where a current consistency group isinitialized to one. The replication management application 112determines (at block 802) whether all storage controls, i.e., theprimary storage control 100 and the secondary storage control 102, havereceived the data updates of the current consistency group. If so, thereplication management application 112 commits the data updates of thecurrent consistency group and for all storage controls sets (at block804) the current pointers to the current consistency group data updates.In certain embodiments, the current pointers may be implemented via datastructures associated with the virtualization tables 208 and/or thepointer tables 508, 510, 512, 602.

The replication management application 112 determines (at block 806)whether all pointers have been updated. If so, the replicationmanagement application deletes (at block 808) the current consistencygroup pointers.

The replication management application 112 increments (at block 810) thecurrent consistency group. For example, if in a first iteration ofblocks 802 to 808 the data updates of the first consistency group areprocessed, then in the second iteration of blocks 802 to 808 the dataupdates of the second consistency group would be processed. Thereplication management application 112 waits (at block 812) for dataupdates of the current consistency group to arrive. If there is no errorwhile waiting then control proceeds to block 802 where the replicationmanagement application 112 determines if all storage controls havereceived the data updates for the current consistency group.

If the replication management application 112 determines (at block 802)that all storage controls have not received the data updates of thecurrent consistency group then the replication management application112 waits (at block 812) for all the data updates of the currentconsistency group to arrive. If an error or disaster strikes whilewaiting (at block 812) the replication management application 112determines (at block 814) the current consistency group on all storagecontrols and then determines (at block 816) the last availableconsistency group in each storage control. The replication managementapplication 112 determines (at block 818) the maximum consistency groupavailable on all storage controls and then updates (at block 820)pointers on all storage controls to correspond to the last availableconsistency group on all storage controls.

If the replication management application 112 determines (at block 806)that all pointers have not been updated then the replication managementapplication 112 waits (at block 822) for all pointers to be updated. Ifthere is no error while waiting, then control returns to block 806 wherethe replication management application 112 determines if all pointershave been updated.

If there is an error while waiting (at block 822) then the replicationmanagement application 112 begins performing (at block 824) a FOR loopfor all the storage controls. The control for the FOR loop is executed(at block 824) for one storage control in every iteration. If the FORloop is incomplete, i.e., not all storage controls have been processed,the replication management application 112 determines (at block 826) ifthe pointers correspond to the current consistency group for the storagecontrol being processed. If so, then the replication managementapplication 112 reverts (at block 828) the pointers to correspond to theprevious consistency group and control proceeds (at block 824) to thenext iteration of the FOR loop with the next storage control.

If the pointers do not correspond (at block 826) to the currentconsistency group then control proceeds (at block 824) to the nextiteration of the FOR loop with the next storage control. At theconclusion of the FOR loop (at block 830) the data in the storagecontrols is consistent with respect to the previous consistency group.

Therefore, the logic of FIG. 8 maintains the data on all storagecontrols consistent with each other and furthermore in the event of anerror or disaster impacting a storage control while updating pointers orreceiving data updates may revert the pointers in the storage controlsto reflect the data updates associated with an earlier processedconsistency group, such that data in the storage controls are consistentwith each other.

These embodiments achieve consistency for asynchronous remote copy byvirtualizing storage systems. A replication management applicationwrites data that has been received but that is not yet consistent withdata in other storage subsystems into unused physical storage. Inresponse to data necessary to provide consistency being received,pointers and tables may be updated at the true target locations to pointto locations in the physical storage where the data has been written.

Therefore, the embodiments do not require a two phase commit at thesecondary storage control to ensure data consistency. In a two phasecommit the data updates may be written into a journal dataset associatedwith the secondary storage control in a first phase and the appropriatedata updates may copied in a second phase when the consistency group iscommitted. The embodiments are implemented without using a journaldataset. In response to a consistency group being committed, pointersare adjusted to point to appropriate locations in physical storage, suchthat the adjusted pointers represent a consistent data set across allstorage controls.

Additionally, in the event of an error or disaster while updatingpointers or waiting for data updates, the embodiments may adjust thepointers in the storage controls to reflect the data updates associatedwith an earlier processed consistency group, such that the data in thestorage controls are consistent with each other.

Furthermore, since the data updates may be kept in disk there is alesser constraint on space utilization or volatility than if the dataupdates are kept in a cache. Additionally, only enough extra disk spaceis needed to contain updates for the number of consistency groups whichare in progress at one time.

Moreover, since no data updates are physically overwritten, in certainembodiments it may be possible to maintain or revert back to multipleprevious versions of consistent data sets in the storage controls.

Additional Implementation Details

The described techniques may be implemented as a method, apparatus orarticle of manufacture using standard programming and/or engineeringtechniques to produce software, firmware, hardware, or any combinationthereof. The term “article of manufacture” as used herein refers to codeor logic implemented in hardware logic (e.g., an integrated circuitchip, Programmable Gate Array (PGA), Application Specific IntegratedCircuit (ASIC), etc.) or a computer readable medium (e.g., magneticstorage medium, such as hard disk drives, floppy disks, tape), opticalstorage (e.g., CD-ROMs, optical disks, etc.), volatile and non-volatilememory devices (e.g., EEPROMs, ROMs, PROMs, RAMs, DRAMs, SRAMs,firmware, programmable logic, etc.). Code in the computer readablemedium is accessed and executed by a processor. The code in whichimplementations are made may further be accessible through atransmission media or from a file server over a network. In such cases,the article of manufacture in which the code is implemented may comprisea transmission media, such as a network transmission line, wirelesstransmission media, signals propagating through space, radio waves,infrared signals, etc. Of course, those skilled in the art willrecognize that many modifications may be made to this configurationwithout departing from the scope of the implementations, and that thearticle of manufacture may comprise any information bearing medium knownin the art.

FIG. 9 illustrates a block diagram of a computer architecture in whichcertain aspects of the invention are implemented. FIG. 9 illustrates oneimplementation of the storage controls 100, 102, a host that includesthe application system 104, and any computational device that includesthe replication management application 112. The storage controls 100,102, the host that includes the application system 104, and anycomputational device that includes the replication managementapplication 112 may implement a computer architecture 900 having aprocessor 902, a memory 904 (e.g., a volatile memory device), andstorage 906 (e.g., a non-volatile storage, magnetic disk drives, opticaldisk drives, tape drives, etc.). The storage 906 may comprise aninternal storage device, an attached storage device or a networkaccessible storage device. Programs in the storage 906 may be loadedinto the memory 904 and executed by the processor 902 in a manner knownin the art. The architecture may further include a network card 908 toenable communication with a network. The architecture may also includeat least one input device 910, such as a keyboard, a touchscreen, a pen,voice-activated input, etc., and at least one output device 912, suchas, a display device, a speaker, a printer, etc.

FIGS. 4-8 describe specific operations occurring in a particular order.Further, the operations may be performed in parallel as well assequentially. In alternative implementations, certain of the logicoperations may be performed in a different order, modified or removedand still implement implementations of the present invention. Morever,steps may be added to the above described logic and still conform to theimplementations. Yet further steps may be performed by a single processor distributed processes.

Although the embodiments as written with respect to an asynchronous peerto peer remote copy, additional embodiments may be used where atwo-phase commit is required for copying. For example, if a database logand table space are both contained with the same virtualization engine,transactions can be written to the log and then the commit can beaccomplished using the virtualization described in the embodiments.There may be a performance improvement for the processing of the database because there is no need to transfer the data to storage for thecommit.

Many of the software and hardware components have been described inseparate modules for purposes of illustration. Such components may beintegrated into a fewer number of components or divided into a largernumber of components. Additionally, certain operations described asperformed by a specific component may be performed by other components.

Therefore, the foregoing description of the implementations has beenpresented for the purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed. Many modifications and variations are possible in light ofthe above teaching. It is intended that the scope of the invention belimited not by this detailed description, but rather by the claimsappended hereto. The above specification, examples and data provide acomplete description of the manufacture and use of the composition ofthe invention. Since many implementations of the invention can be madewithout departing from the spirit and scope of the invention, theinvention resides in the claims hereinafter appended.

1. A system for copying storage, comprising: a memory; and a processorcoupled to the memory, wherein the processor performs operations, theoperations comprising: receiving, at a first unit, data updates from asecond unit; storing the data updates in a plurality of physical storagelocations associated with the first unit, wherein the received dataupdates are stored only once in the plurality of physical storagelocations associated with the first unit; and generating links to atleast one of the plurality of physical storage locations to achieveconsistent data between the first unit and the second unit, wherein theoperations further comprise: (i) determining if the stored data updatesform a consistency group, prior to generating the links, wherein theconsistency group is a set of data updates in which the set of dataupdates corresponds to a plurality of storage volumes, wherein the setof data updates must be written together in order to maintain mutualdata consistency among data included in each storage volume of theplurality of storage volumes; (ii) determining the at least one physicalstorage location that commits the consistency group, wherein virtualstorage associated with the first unit links to the determined at leastone physical storage location, wherein a consistency group pointer tableincludes entries for a virtual block and a physical block; and (iii)releasing unlinked physical storage locations to be used for storingsubsequent data updates, wherein the first unit is a secondary storagecontrol, wherein the second unit is a primary storage control, whereinthe secondary storage control and the primary storage control comprise aplurality of storage controls, and wherein in response to receiving anerror while waiting for all links to be updated, performing for eachstorage control of the plurality of storage controls being processed:(a) determining, by a replication management application, if selectedlinks correspond to a current consistency group for the storage controlbeing processed; and (b) reverting the selected links to correspond to aprevious consistency group, in response to determining by thereplication management application that the selected links correspond tothe current consistency group for the storage control being processed.2. The system of claim 1, wherein the secondary storage control iscoupled to a secondary storage and the primary storage control iscoupled to a primary storage, wherein the plurality of physical storagelocations are associated with the secondary storage, and wherein thedata updates are received asynchronously at the first unit.
 3. Thesystem of claim 1, wherein an application sends input/output requests tothe primary storage control, wherein the data updates correspond tooutput requests from the application, and wherein the data updates arestored only once at the secondary storage control, wherein the secondarystorage control can substitute the primary storage control in respondingto the input/output requests from the application at any point in time,and wherein data in the primary and secondary storage controls areconsistent at all points in time.
 4. The system of claim 1, furthercomprising: maintaining a data structure that maps virtual storagelocations to the at least one of the plurality of physical storagelocations, wherein the generated links are associated with the datastructure, and wherein a plurality of applications are capable ofperforming input/output operations with the virtual storage locations,wherein a plurality of consistency group pointers, consistency grouppointer tables, and relative times for data updates are maintained. 5.The system of claim 1, further comprising: maintaining data structuresrepresenting consistency groups corresponding to the data updates,wherein the maintained data structures are capable of pointing to theplurality of physical storage locations, wherein a plurality ofconsistency group pointers, consistency group pointer tables, andrelative times for data updates are maintained; and deleting a firstdata structure that represents a first consistency group in response tofirst data updates associated with the first consistency group beingcommitted.
 6. A computer readable storage medium including code forcopying to a first unit from a second unit, wherein the code whenexecuted by a machine is capable of causing operations, the operationscomprising: receiving, at the first unit, data updates from the secondunit; storing the data updates in a plurality of physical storagelocations associated with the first unit, wherein the received dataupdates are stored only once in the plurality of physical storagelocations associated with the first unit; and generating links to atleast one of the plurality of physical storage locations to achieveconsistent data between the first unit and the second unit, wherein theoperations further comprise: (i) determining if the stored data updatesform a consistency group, prior to generating the links, wherein theconsistency group is a set of data updates in which the set of dataupdates corresponds to a plurality of storage volumes, wherein the setof data updates must be written together in order to maintain mutualdata consistency among data included in each storage volume of theplurality of storage volumes; (ii) determining the at least one physicalstorage location that commits the consistency group, wherein virtualstorage associated with the first unit links to the determined at leastone physical storage location, wherein a consistency group pointer tableincludes entries for a virtual block and a physical block; and (iii)releasing unlinked physical storage locations to be used for storingsubsequent data updates, wherein the first unit is a secondary storagecontrol, wherein the second unit is a primary storage control, whereinthe secondary storage control and the primary storage control comprise aplurality of storage controls, and wherein in response to receiving anerror while waiting for all links to be updated, performing for eachstorage control of the plurality of storage controls being processed:(a) determining, by a replication management application, if selectedlinks correspond to a current consistency group for the storage controlbeing processed; and (b) reverting the selected links to correspond to aprevious consistency group, in response to determining by thereplication management application that the selected links correspond tothe current consistency group for the storage control being processed.7. The computer readable storage medium of claim 6, wherein thesecondary storage control is coupled to a secondary storage and theprimary storage control is coupled to a primary storage, wherein theplurality of physical storage locations are associated with thesecondary storage, and wherein the data updates are receivedasynchronously at the first unit.
 8. The computer readable storagemedium of claim 6, wherein an application sends input/output requests tothe primary storage control, wherein the data updates correspond tooutput requests from the application, and wherein the data updates arestored only once at the secondary storage control, wherein the secondarystorage control can substitute the primary storage control in respondingto the input/output requests from the application at any point in time,and wherein data in the primary and secondary storage controls areconsistent at all points in time.
 9. The computer readable storagemedium of claim 6, further comprising: maintaining a data structure thatmaps virtual storage locations to the at least one of the plurality ofphysical storage locations, wherein the generated links are associatedwith the data structure, and wherein a plurality of applications arecapable of performing input/output operations with the virtual storagelocations, wherein a plurality of consistency group pointers,consistency group pointer tables, and relative times for data updatesare maintained.
 10. The computer readable storage medium of claim 6,further comprising: maintaining data structures representing consistencygroups corresponding to the data updates, wherein the maintained datastructures are capable of pointing to the plurality of physical storagelocations, wherein a plurality of consistency group pointers,consistency group pointer tables, and relative times for data updatesare maintained; and deleting a first data structure that represents afirst consistency group in response to first data updates associatedwith the first consistency group being committed.